Near-infrared properties of i-drop galaxies in the Hubble Ultra Deep Field |
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| Authors: | Elizabeth R Stanway Richard G McMahon Andrew J Bunker |
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| Institution: | Institute of Astrophysics, University of Cambridge, Madingley Road, Cambridge CB3 0HA;School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL |
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| Abstract: | We analyse near-infrared Hubble Space Telescope ( HST )/Near-Infrared Camera and Multi-Object Spectrometer F 110 W ( J ) and F 160 W ( H ) band photometry of a sample of 27 i '-drop candidate z ? 6 galaxies in the central region of the HST /Advanced Camera for Surveys Ultra Deep Field . The infrared colours of the 20 objects not affected by near neighbours are consistent with a high-redshift interpretation. This suggests that the low-redshift contamination of this i '-drop sample is smaller than that observed at brighter magnitudes, where values of 10–40 per cent have been reported. The J – H colours are consistent with a slope flat in fν ( fλ ∝λ?2) , as would be expected for an unreddened starburst. However, there is evidence for a marginally bluer spectral slope ( fλ ∝λ?2.2) , which is perhaps indicative of an extremely young starburst (～10 Myr old) or a top heavy initial mass function and little dust. The low levels of contamination, median photometric redshift of z ～ 6.0 and blue spectral slope, inferred using the near-infrared data, support the validity of the assumptions in our earlier work in estimating the star formation rates, and that the majority of the i -drop candidates galaxies lie at z ～ 6 . |
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| Keywords: | galaxies: evolution galaxies: formation galaxies: high-redshift galaxies: starburst |
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